The present invention relates to apparatus employing recursive estimation for determining percentiles, being the value of an analogue signal level exceeded for a specified percentage of a period of time. In particular the invention has advantageous application in determining the sound level exceeded for a specified proportion of a predetermined period of time during which the measurement is made. This may be achieved by suitable connection of the analogue output of a sound level meter to apparatus in accordance with the invention.
It will be appreciated that the applicability of the present invention is not solely in the field of sound measurement. The apparatus of the invention may be employed in any application where a variation in a quantity requires analysis statistically to determine percentiles and where that quantity can be represented by an analogue signal. However, the invention is described in relation to the field of acoustic measurement for reasons of convenience.
Current techniques for determining percentiles from acoustic data require a determination of the sample histogram of the acoustic data. Thereafter, a cumulative distribution function is produced by statistical methods so that percentiles may then be calculated by interpolation. It will be appreciated that current techniques require time and effort to arrive at the appropriate percentiles which constitute the figures used by relevant authorities such as council and government bodies as a direct measurement of the level of a noise pollution problem at a particular location. Accordingly, it is most desirable that, for the purpose of assessing local noise pollution problems, there be a device for measuring the relevant noise statistics.